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Sailing in tide..quiz.

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Sam.Spoons View Drop Down
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 9:55pm
Sorry Doug, I was trying to answer mozzy's 'supplementary question'  Smile Not sure I have the answer right but based on 'conveyer belt' theory?

Edited by Sam.Spoons - 03 Oct 17 at 9:56pm
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 10:04pm
Originally posted by mozzy

Once I did lay a finish mark that dried out... oops, I did get a fair bit of stick for that. But there is no rule that the course has to be on the water!

I remember Raceboards Open Meetings at Morecambe many years ago, I got there early one year and helped set the course marks with the aid of a wheelbarrow (and, incidentally, collect them the same way after the event)  Tongue happy days......
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 10:04pm
Originally posted by mozzy


Originally posted by Sam.Spoons

Assuming the tide slackens across the whole course? No windshifts? And they were sailing at exactly the same speed? B would have to take avoiding action to avoid hitting A (still on Starboard)?

Spot on! A would hold a 1 metre is lead and B would have to avoid. 


Agreed, but then B could still short tack, onto the starboard layline and force A behind and round first

Edited by iGRF - 03 Oct 17 at 10:05pm
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Post Options Post Options   Quote A2Z Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 10:14pm
Originally posted by Sam.Spoons

Sorry Doug, I was trying to answer mozzy's 'supplementary question'  Smile Not sure I have the answer right but based on 'conveyer belt' theory?
This conveyor belt theory. Why is it assumed all boats drift downtide at the speed of the current?  Isn't that like assuming all boats can run downwind at windspeed?
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Post Options Post Options   Quote mozzy Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 10:22pm
Originally posted by A2Z

Originally posted by Sam.Spoons

Sorry Doug, I was trying to answer mozzy's 'supplementary question'  Smile Not sure I have the answer right but based on 'conveyer belt' theory?
This conveyor belt theory. Why is it assumed all boats drift downtide at the speed of the current?  Isn't that like assuming all boats can run downwind at windspeed?
All boats do drift down tide at the speed of the current. Unless you're sailing them through the water. In which case they will move in a direction over land which is the sum of those two vectors (the tide and the sailing).

Trust me, when the wind drops to nothing, and the tide is flushing out the harbour, all the boats, 49er to oppie, all drift out the harbour with equal hopelessness! 


Edited by mozzy - 03 Oct 17 at 10:24pm
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 10:38pm
In a flat calm that must the case (well actually won't they drift slightly slower than the tide due to air resistance)? TBF that might slow them by a fraction of a knot........ "Pedant's rule OK?"
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Post Options Post Options   Quote A2Z Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 17 at 10:51pm
As a pondie I'm clueless but intrigued.
Boats aren't rigidly attached to the water, the water flows past and hydrodynamic forces are imparted.  I can't see why they should be the same regardless of the type of boat, in which case I can't see why they drift off at the same (current) speed. Therefore, if not all boats slip at 1.5kts in the example above, the winning tactics might not always be the same?
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 7:25am
They don't, amount of boat in water, plus wind resistance, handicap fleet, different boats react differently.
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Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 7:41am
But the wind resistance is just the gaseous fluid motion bit of the vector.

In a flat calm the rate of drift is the same.  Seen it in the Cherbourg Race couple of years ago.  Heaps of different boats drifting together.  Possibly you could have assessed that the much heavier ones had momentum and took longer to start drifting the other way when the tide turned.

Or that might have been the beer we were drinking for breakfast..... 
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 17 at 8:49am
Surely, in a flat calm, as soon as the boat starts to drift with the current an apparent wind equal to the speed of the current will be generated? E.g. in a 3 knot tide with no actual wind (as measured by an anchored boat) any boat drifting with the current will feel a 3 knot breeze?
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